More particularly, the invention concerns a device for health monitoring of an area of a structural element comprising at least one dielectric material of dielectric permittivity εr comprising:    (A) means of emission of electromagnetic radiation extending in a direction, the said electromagnetic field generating an electric field in the area, and    (B) detection means suitable for measuring a first measured component of an electric field, along a first direction of detection.
The structural elements in question are typically materials made of resin reinforced with glass fibres or carbon fibres, forming part of the structure, for example of a vehicle such as a motor vehicle, an aircraft, a railway vehicle, or the like, for which the weight constraints are paramount.
Such a device has already been used with success in the past to determine whether such a structural element exhibited a defect, for example of a mechanical or chemical nature, or the like. Such an example of an application is described in “Electromagnetic health monitoring system for composite materials”, Lemistre and Balageas, in Matériaux et Techniques, special issue 2002, published by SIRPE, Paris, pg 29-32.
In this article, the electromagnetic field is, for structures comprising carbon fibres, a magnetic field locally equivalent to the magnetic field emitted by a dipole extending along a given direction of the structural element and is emitted by two linear conducting tracks extending in this direction and traversed in opposite senses by an electric current. The electric field is measured orthogonally to this direction in the plane of the structure. The information thus gleaned is useful for determining whether the structure does or does not exhibit a defect.
For structures comprising glass fibres or simply a resin, the exciter field is an electromagnetic field emitted by the tracks extending likewise in this direction.
Such a device makes it possible to qualify the presence or otherwise of a structural defect in the structure under study, but does not make it possible to determine the gravity of the defect. In the presence of a defect, the user of the device will not know what to do: wait or replace the structure (thereby guaranteeing safety to the detriment of cost) even if the defect is not perhaps penalizing per se for the structure in its daily application.